Module: DescriptiveStatistics::Spread

Included in:
AllMethods
Defined in:
lib/descriptive-statistics/spread.rb

Instance Method Summary collapse

Instance Method Details

#population_standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 25

def population_standard_deviation
  return if length < 2
  Math.sqrt(population_variance)
end

#population_variance ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 9

def population_variance
  return if length < 1
  sum = self.inject(0) {|accumulator, value| accumulator + (value - mean) ** 2 }
  sum / length.to_f
end

#relative_standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 20

def relative_standard_deviation
  return if length < 1
  (population_standard_deviation / mean) * 100.0
end

#standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 15

def standard_deviation
  return if length < 2
  Math.sqrt(variance)
end

#variance ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 3

def variance
  return if length < 1
  sum = self.inject(0) {|accumulator, value| accumulator + (value - mean) ** 2 }
  sum / (length.to_f - 1)
end